Recent Doppler ultrasound technological advances have demonstrated the unique capability to detect formed element and gas microemboli in the middle cerebral artery (MCA). These microemboli detected in the MCA have been implicated in a variety of cerebral abnormalities and are associated with vascular pathologies and interventional procedures in vessels from the heart to the brain. This proposal is to explore the feasibility of dual carrier frequency Doppler technology for determining size and composition (gas or particulate) of MCA microemboli, in the presence of beam refraction at tissue interfaces such as temporal bone to brain and brain to blood. Theoretical simulations and in vitro studies, utilizing human temporal bone and a rabbit model of the MCA, will be conducted to determine the extent of beam refraction in the MCA. Methods to mitigate effects of refraction on ability to size and characterize microemboli will then be explored. This technology is important for reducing the incidence of stroke associated with various cardiovascular pathologies and surgery of the heart and of the carotid arteries. A device for discrimination of size and composition of microemboli in the cerebral arteries represents a major commercial market potential. PROPOSED COMMERCIAL APPLICATION The instrument to be developed in this project will detect and characterize embolization in a variety of cardiovascular pathologies and surgical situations. The instrument will be aimed at the perioperative, radiology ultrasound, echocardiography, vascular lab and emergency markets.